A typical gate insert of an injection mold includes a base member that defines a nozzle interface and a gate. The nozzle interface receives, in use, a nozzle of a melt distribution system such as a hot runner. The nozzle is typically heated, in use, by a heater. The gate is configured to fluidly link a melt channel of the nozzle with a molding cavity.
Good temperature control of the gate is an important aspect to efficiently mold a molded article of high quality. The ability to quickly and accurately control gate temperature has a material affect on aspects of injection molding that include cycle time, prevention of pre-mature gate freeze-off, preventing stringing/drooling from gate, minimizing gate vestige, ensuring a good temperature control of resin into mold, and the minimization of pressure drop. The migration of heat between the nozzle interface (heated by virtue of contact with the heated nozzle) is a factor, amongst others, that influences gate temperature control.
A known approach to gate temperature control has been to provide a high thermal conductivity nozzle with a low thermal conductivity gate seal, and a responsive nozzle heat control structure (e.g. a heater, heater controller, and temperature sensor arrangement) wherein the nozzle has a strict thermal profile.
Another known approach to gate temperature control has been to provide an insulating space between the nozzle and the gate insert within which air or solidified resin is provided to insulate the gate.
Another known approach to gate temperature control has been to provide a fluid channel around the gate insert that functions to cool the gate.
Another known approach to gate temperature control has been to provide an internally heated nozzle tip that functions to heat the gate area only during intervals of injection of molding material into the molding cavity.
Another known approach to gate temperature control has been to provide a low conductivity insert for insulating the gate from the mold.
Another known approach to gate temperature control has been to provide a high conductivity insert that is configured to conduct heat from the gate to cooling channels.
Even with these, and other, approaches available to those skilled in the art with which to control gate temperature, research and investigation has continued into new and improved structures and/or steps for ever more precise gate temperature control. One such investigation undertaken by the inventor has been into the application of direct energy conversion devices (i.e. devices that directly convert thermal energy into electrical energy—like a heat pump) for the new use of controlling gate temperature in an injection mold.
Examples of prior use of direct energy conversion devices, of the thermoelectric type, in the field of injection molding include the following:
U.S. Pat. No. 3,661,487 (Inventor: SUSIN, Victor et al.; Published: May 9, 1972) describes that high pressure tubing for carrying a plasticized material can be surrounded by thermoelectric material rather than fluid carrying tubing. The thermoelectric material is placed contiguous to a runner plate which is maintained at a higher temperature than the temperature of the runner. The thermoelectric material takes advantage of the Peltier effect and comprises junctions of two dissimilar metals. When electric current passes through the junctions in a first direction then one junction cools while the other heats. A reversal of current causes the warm junction to cool and the cool junction to heat. The thermoelectric material is operated to maintain the plasticized material at a desired temperature since a power supply can be used to selectively supply current in a forward or reverse direction as desired to heat or cool the plasticized material as required.
U.S. Pat. No. 3,804,362 (Inventor: STROMBLAND, John; et al.; Published: Apr. 16, 1974) describes dividing a part of a casting mould into two thermally insulated sections, one being a part of the actual mould portion having a moulding space, and that between the sections so-called Peltier elements are arranged, with the heat-emitting and heat-absorbing parts, respectively, in contact with each section, and that the current direction through the elements is reversible in order to change from cooling to heating, or vice versa, of the moulding space section. The operation of the Peltier element makes it possible rapidly to raise or lower the temperature in the mould and thus achieve rapid production with high quality.
U.S. Pat. No. 5,176,839 (Inventor: KIM, Bang et al.; Published: Jan. 5, 1993) describes core halves of a mold having cooling lines for receiving a cooling fluid to reduce cycle time. In addition, a thermoelectric device may be disposed between the core halves and respective insulating layers to provide fast cooling, thereby reducing cycle time.
U.S. Pat. No. 6,238,613 (Inventor: BATCHELDER, John, Samuel; Published: May 29, 2001) describes an extrusion device for extrusion of thermoplastic in a predetermined spatial pattern under computer control. A heat sink cools a valve region of a flow channel within the apparatus to a temperature below the lowest flowable temperature of the thermoplastic. A heater thermally contacting the valve region creates a thermal valve. The heat sink may be maintained at a desired low temperature using a flowing thermal fluid, such as water, or using any other active cooling technique known to those skilled in the art, such as air cooling, thermoelectric cooling, refrigeration or conduction cooling.
More generally, the structure and operation of thermoelectric devices are discussed, for example, with reference to the following:
U.S. Pat. No. 5,228,923 (Inventor: HED, Aharon; Published: Jul. 20, 1993) describes a structure and steps to withdraw large quantities of heat from a small surface with the use of planar thermoelectric cells. The structure provides a cylindrical refrigerator positioned concentrically within a closed end cylindrical structure. A heat exchange fluid is pumped through an inner hollow toward a closed end plate (cold plate) of an external cylinder and returns in the space between a bracing structure and an outer cylinder.
United States Patent Application No. 2004/0076214 (Inventor: BELL, Lon K et al.; Published: Mar. 22, 2004) describes a device for cooling and/or heating applications that includes thermoelectric elements, or modules, that are sandwiched between heat exchangers. The thermoelectric elements are advantageously oriented such that for any two elements sandwiching a heat exchanger, the same temperature type side faces the heat exchanger. A working medium is passed sequentially through at least two heat exchangers so that the cooling or heating provided is additive on the working medium.
United States Patent Application No. 2005/172991 (Inventor: ARAI, Tomohisa et al.; Published: Aug. 11, 2005) describes a thermoelectric element mountable to an object to be cooled, the thermoelectric element having a first heat transmitting member integrated with a heat radiating electrode and a second heat transmitting member integrated with a heat absorbing electrode are respectively provided to protrude outside the heat radiating electrode, further to a space outside the heat radiation side support member. The space is a radiation space in which a cooling medium exists.
Other examples of direct energy conversion devices include thermionic and thermotunneling devices, which are described, for example, with reference to the following:
U.S. Pat. No. 5,675,972 (Inventor: EDELSON, Jonathan Sidney; Published: Oct. 14, 1997) describes vacuum diode-based devices, including a vacuum diode heat pump and vacuum thermionic generators, are described in which the electrodes are coated with an electride.
U.S. Pat. No. 6,876,123 (Inventor: MARTINOVSKY, Artemy et al.; Published: Apr. 5, 2005) describes a thermotunneling converter is disclosed comprising a pair of electrodes having inner surfaces substantially facing one another, and a spacer or plurality of spacers positioned between the two electrodes, having a height substantially equal to the distance between the electrodes, and having a total cross-sectional area that is less than the cross-sectional area of either of the electrodes.
In the description that follows, the inventor will describe a novel structure and steps for gate temperature control in a gate insert that makes use of a direct energy conversion device.